1. Field of the Invention.
The present invention relates to apparatus for evaluating the wall thickness of round bottles to make certain that no incorrect thickness is determined due to interference caused by a bottle seam.
2. Description of the Related Art
Round bottles are conventionally rolled along an elongated capacitance sensor which senses the capacitance and hence thickness of the wall of the bottle. An Oscillator is used to determine this capacitance and generate a voltage which can be converted to dimensional data representative of the wall thickness. Whenever the bottle seam rolls past the capacitance sensor, a false "thick spot" will be generated as the seam approaches. A "thin spot" signal will be generated once the seam is at the head and immediately after. This data must be ignored. State of the art systems detect the seam by determining the rate of change or differential of periodic thickness samples. Whenever this differential exceeds a selected threshold, a seam has been detected and a timer which has a fixed period is started. Subsequent samples received during the window of this timer will be ignored.
A problem with the current state-of-the-art is that it is set for the machine to operate at a certain speed. When machine speed is changed, these settings are incorrect. The current state-of-the-art also does not ignore incorrect readings caused by an approaching seam.
It is an object of the present invention to provide an improved apparatus for defining the window during which sampled data will be ignored in the vicinity of this seam. This invention will allow us to ignore incorrectly sampled data before the seam is detected as well as after, regardless of machine speed.
Other objects and advantages of the present invention will become apparent from the following portion of the specification and from the following drawings which illustrate in accordance with the mandate of the patent statues a presently preferred embodiment incorporating the principles of the invention.